NITRA TES IN CA VE EA R THS 237 



contain insoluble organic matter or more organic matter than is 

 indicated by the amount of nitrogen and chlorine shown by Mr. 

 Hess' analyses. This objection, apparently based on inspection 

 of the specimens and a single analysis, cannot therefore be con- 

 sidered proven. The third objection made by Mr. Hess to the 

 origin of nitrates in the cavern itself is that while the cave earth 

 and the bat guano contain approximately equal quantities of 

 phosphates, the soluble phosphate is much less in the underly- 

 ing earth than in the overlying guano. This, however, is merely 

 an illustration of a phenomenon with which all phosphate manu- 

 facturers are familiar, viz., the "reversion" of the soluble to the 

 insoluble phosphate by virtue of which a very large percentage 

 of the " available " or soluble acid calcium phosphate of a" super- 

 phosphate" when applied to the soil, changes to various insolu- 

 ble phosphates. 1 It does not appear, then, that any of the above 

 objections are in any sense conclusive. 



In support of the external origin of the nitrates, Mr. Hess 

 calls attention to the fact that the leachings from the surface 

 subsoil contain nitrates in small quantity. He also attempts to 

 show by analyses that the soluble portions of the niter earth 

 might be the concentration of the leachings from surface soils, 

 although the figures he gives appear to prove the reverse. Inas- 

 much as both the niter earth and the surface soil are both (in 

 the Kentucky and Indiana caves) residual soils from limestone, 

 contaminated with organic matter, a general similarity in conse- 

 quence of similarity of origin is to be expected and is found. 

 But if the soluble salts of the niter earths are the soluble salts 

 transported from the overlying soil, more than a general 

 resemblance should appear. After due allowance is made for 

 compounds which will not redissolve the two should be prac- 

 tically identical if the analyses correctly represent the average 

 constitution of the mixtures in question. As printed, Mr. 

 Hess' analyses do not admit of ready comparison. If the 

 analysis which he gives (p. 131) of subsoil over Mammoth 

 Cave and of the cave earth directly below are recalculated so as 



1 Wyatt : Phosphates of America. 



